Normally, a rigid substrate is used as a substrate to make a thin-film laminated body such as a semiconductor thin film. However, a flexible substrate such as a plastic film is often used for the purpose of cost reduction and improving the productivity in which the substrate is handled using a roll.
For example, Patent Document 1 discloses a device that uses a plurality of film-forming chambers to stack a plurality of thin films of different qualities on each of belt-like flexible substrates that are supplied from an unwinding roll, while conveying the flexible substrates at a predetermined pitch.
As this type of flexible substrate conveying device, there is a type that transports a flexible substrate with a width direction thereof matched with a horizontal direction, and a type that transports a flexible substrate while having the flexible substrate upright with one end part thereof up in a width direction of the substrate. The latter has a smaller installation area than the former and is more advantageous than the former in that a surface of the flexible substrate is not contaminated easily.
However, the longer the span for conveying the flexible substrate, the more complicated it is no maintain a constant conveyance height of the flexible substrate against the gravity, weighing down the flexible substrate or frequently generating wrinkles on the surface of the flexible substrate.
For this reason, there has been conventionally proposed a substrate retaining device for maintaining a conveyance height of a flexible substrate.
FIG. 14 shows an example of a substrate retaining device of a conventional flexible substrate conveying device.
As shown in FIG. 14, a conventional substrate retaining device 90 has a pair of grip rollers 91, 92 for sandwiching an end part on the upper side of a flexible substrate 93, and a roller fixing part 94 for fixing the pair of grip rollers 91, 92.
Surfaces of the pair of grip rollers 91, 92 are covered with elastic bodies 91a, 92a, respectively. A pair of roller fixing shafts 95, 96 is attached to the roller fixing part 94. The pair of grip rollers 91, 92 is attached rotatably to lower parts 95a, 96a of the roller fixing shafts 95, 96. On the other hand, an upper end 95b of the roller fixing shaft 95 is fixed to the roller fixing part 94, and an upper end 96b of the other roller fixing shaft 96 is attached rotatably to the roller fixing part 94 via a hinge 97. In this manner, the pair of grip rollers 91, 92 is configured to contact with and separate from each other by causing the roller fixing shaft 96 to turn around the hinge 97.
Upper surfaces of both of the roller fixing shafts 95, 96 are provided with spring attachment parts 95c, 96c. The spring attachment parts 95c, 96c are coupled to each other by a tension spring 98. This tension spring 98 generates an urging force in a pressure contact direction of the pair of grip rollers 91, 92. One end of the tension spring 98 is attached to the spring attachment part 95c via an urging force adjusting screw 99. The substrate retaining device 90 can adjust a pressure generated between the pair of grip rollers 91, 92, by rotating the urging force adjusting screw 99.    Patent Document 1: Japanese Patent Application Publication No. 2005-72408
However, in the conventional substrate retaining device 90 described above, frictional forces of the elastic bodies 91a, 92a on the surface of the grip rollers 91, 92 become weak over time, which might result in a decrease of gripping forces of the grip rollers 91, 92. In this case, the flexible substrate 93 can be loose and weighed down from the pair of grip rollers 91, 92.
Moreover, in the conventional substrate retaining device 90 described above, constantly applying a large pressure between the grip rollers 91, 92 can change the diameter the grip rollers 91, 92, In this case, a lifting force applied to the flexible substrate 93 drops, and a conveyance height of the flexible substrate 93 cannot be kept constant.